// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.

#include <math.h>
#include <stdio.h>
#include "port/port.h"
#include "util/histogram.h"

namespace leveldb {

    const double Histogram::kBucketLimit[kNumBuckets] = {
            1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 45,
            50, 60, 70, 80, 90, 100, 120, 140, 160, 180, 200, 250, 300, 350, 400, 450,
            500, 600, 700, 800, 900, 1000, 1200, 1400, 1600, 1800, 2000, 2500, 3000,
            3500, 4000, 4500, 5000, 6000, 7000, 8000, 9000, 10000, 12000, 14000,
            16000, 18000, 20000, 25000, 30000, 35000, 40000, 45000, 50000, 60000,
            70000, 80000, 90000, 100000, 120000, 140000, 160000, 180000, 200000,
            250000, 300000, 350000, 400000, 450000, 500000, 600000, 700000, 800000,
            900000, 1000000, 1200000, 1400000, 1600000, 1800000, 2000000, 2500000,
            3000000, 3500000, 4000000, 4500000, 5000000, 6000000, 7000000, 8000000,
            9000000, 10000000, 12000000, 14000000, 16000000, 18000000, 20000000,
            25000000, 30000000, 35000000, 40000000, 45000000, 50000000, 60000000,
            70000000, 80000000, 90000000, 100000000, 120000000, 140000000, 160000000,
            180000000, 200000000, 250000000, 300000000, 350000000, 400000000,
            450000000, 500000000, 600000000, 700000000, 800000000, 900000000,
            1000000000, 1200000000, 1400000000, 1600000000, 1800000000, 2000000000,
            2500000000.0, 3000000000.0, 3500000000.0, 4000000000.0, 4500000000.0,
            5000000000.0, 6000000000.0, 7000000000.0, 8000000000.0, 9000000000.0,
            1e200,
    };

    void Histogram::Clear() {
        min_ = kBucketLimit[kNumBuckets - 1];
        max_ = 0;
        num_ = 0;
        sum_ = 0;
        sum_squares_ = 0;
        for (int i = 0; i < kNumBuckets; i++) {
            buckets_[i] = 0;
        }
    }

    void Histogram::Add(double value) {
        // Linear search is fast enough for our usage in db_bench
        int b = 0;
        while (b < kNumBuckets - 1 && kBucketLimit[b] <= value) {
            b++;
        }
        buckets_[b] += 1.0;
        if (min_ > value) min_ = value;
        if (max_ < value) max_ = value;
        num_++;
        sum_ += value;
        sum_squares_ += (value * value);
    }

    void Histogram::Merge(const Histogram &other) {
        if (other.min_ < min_) min_ = other.min_;
        if (other.max_ > max_) max_ = other.max_;
        num_ += other.num_;
        sum_ += other.sum_;
        sum_squares_ += other.sum_squares_;
        for (int b = 0; b < kNumBuckets; b++) {
            buckets_[b] += other.buckets_[b];
        }
    }

    double Histogram::Median() const {
        return Percentile(50.0);
    }

    double Histogram::Percentile(double p) const {
        double threshold = num_ * (p / 100.0);
        double sum = 0;
        for (int b = 0; b < kNumBuckets; b++) {
            sum += buckets_[b];
            if (sum >= threshold) {
                // Scale linearly within this bucket
                double left_point = (b == 0) ? 0 : kBucketLimit[b - 1];
                double right_point = kBucketLimit[b];
                double left_sum = sum - buckets_[b];
                double right_sum = sum;
                double pos = (threshold - left_sum) / (right_sum - left_sum);
                double r = left_point + (right_point - left_point) * pos;
                if (r < min_) r = min_;
                if (r > max_) r = max_;
                return r;
            }
        }
        return max_;
    }

    double Histogram::Average() const {
        if (num_ == 0.0) return 0;
        return sum_ / num_;
    }

    double Histogram::StandardDeviation() const {
        if (num_ == 0.0) return 0;
        double variance = (sum_squares_ * num_ - sum_ * sum_) / (num_ * num_);
        return sqrt(variance);
    }

    std::string Histogram::ToString() const {
        std::string r;
        char buf[200];
        snprintf(buf, sizeof(buf),
                 "Count: %.0f  Average: %.4f  StdDev: %.2f\n",
                 num_, Average(), StandardDeviation());
        r.append(buf);
        snprintf(buf, sizeof(buf),
                 "Min: %.4f  Median: %.4f  Max: %.4f\n",
                 (num_ == 0.0 ? 0.0 : min_), Median(), max_);
        r.append(buf);
        r.append("------------------------------------------------------\n");
        const double mult = 100.0 / num_;
        double sum = 0;
        for (int b = 0; b < kNumBuckets; b++) {
            if (buckets_[b] <= 0.0) continue;
            sum += buckets_[b];
            snprintf(buf, sizeof(buf),
                     "[ %7.0f, %7.0f ) %7.0f %7.3f%% %7.3f%% ",
                     ((b == 0) ? 0.0 : kBucketLimit[b - 1]),      // left
                     kBucketLimit[b],                           // right
                     buckets_[b],                               // count
                     mult * buckets_[b],                        // percentage
                     mult * sum);                               // cumulative percentage
            r.append(buf);

            // Add hash marks based on percentage; 20 marks for 100%.
            int marks = static_cast<int>(20 * (buckets_[b] / num_) + 0.5);
            r.append(marks, '#');
            r.push_back('\n');
        }
        return r;
    }

}  // namespace leveldb
